21: GENE EXPRESSION

Question 1

What are the three components of a DNA nucleotide?

Answer 1

Deoxyribose, Organic base, Phosphate

Question 2

What is transcription?

Answer 2

It takes place in the nucleus of the cell and involves the formation of pre-mRNA with a complementary sequence of bases to the DNA.

Question 3

Why is the mRNA transcribed from a gene shorter than the gene itself?

Answer 3

pre-mRNA is spliced to remove introns and leave only the coding exons.

Question 4

List the main differences between DNA and mRNA.

Answer 4

• DNA: double polynucleotide chain
• mRNA: single
• DNA: largest molecule of the three
• mRNA: smaller than DNA, bigger than tRNA
• DNA: double helix shape
• mRNA: single linear strand
• DNA: pentose sugar is deoxyribose
• mRNA: ribose
• DNA: bases found are A, T, C and G
• mRNA: bases found are A, U, C and G
• DNA: found in nucleus of cell
• mRNA: nucleus and cytoplasm
• DNA: chemically stable
• mRNA: unstable

Question 5

At what two stages can gene expression be controlled?

Answer 5

Transcription and Translation

Question 6

What are transcriptional factors?

Answer 6

They are found in the cytoplasm, move into the nucleus, and bind to specific base sequences of the DNA to stimulate transcription.

Question 7

How does oestrogen affect gene transcription?

Answer 7

Oestrogen enters the cell by simple diffusion, binds to a transcriptional factor, changes its shape, releases an inhibitor molecule, and allows transcription to be initiated.

Question 8

What is the function of the inhibitor molecule in gene transcription?

Answer 8

It prevents the transcriptional factor from binding to the DNA promoter region, inhibiting transcription.

Question 9

What is RNA interference (RNAi)?

Answer 9

It inhibits gene expression at the translation stage by cutting specific mRNA molecules.

Question 10

What are the potential applications of RNAi in scientific research?

Answer 10

• Identifying the role of genes in biological pathways
• Prevention of genetic conditions

Question 11

Why are all cells in an organism genetically identical?

Answer 11

They are all produced by mitosis following fertilisation of an egg cell.

Question 12

What are the two main features of stem cells?

Answer 12

• Undifferentiated but can differentiate into specialised cells
• Can replace themselves

Question 13

What are totipotent stem cells?

Answer 13

Stem cells that can differentiate into any type of body cell, including placental cells.

Question 14

What are pluripotent stem cells?

Answer 14

Stem cells found in embryos that can differentiate into all tissue types except placental cells.

Question 15

What are multipotent stem cells?

Answer 15

Stem cells found in many tissues of mature mammals that can differentiate into a limited number of different cell types.

Question 16

What are unipotent stem cells?

Answer 16

Stem cells that can only differentiate into one type of cell or tissue.

Question 17

What are induced pluripotent stem cells (iPS)?

Answer 17

Pluripotent stem cells produced from differentiated adult body cells using specific protein transcriptional factors.

Question 18

What is the purpose of using stem cells in treating human disorders?

Answer 18

To replace damaged cells or tissues in a patient.

Question 19

What are the advantages of using pluripotent stem cells?

Answer 19

Can differentiate into any type of body cell.

Question 20

What are the disadvantages of using embryonic stem cells?

Answer 20

Risk of rejection and ethical issues due to being sourced from embryos.

Question 21

What are ethical concerns regarding embryonic stem cells?

Answer 21

• Potential for life in embryos
• Manipulation or destruction of embryos is unethical
• Consent issues for using embryos

Question 22

What is epigenetics?

Answer 22

Heritable changes in gene function without changes to the base sequence of DNA.

Question 23

What is the epigenome?

Answer 23

Comprises all the chemical tags added to a person’s genome.

Question 24

What is the effect of acetylation on histones?

Answer 24

Acetyl groups bind to histone proteins, reducing condensation of chromatin and making promoter regions accessible.

Question 25

What happens during decreased acetylation?

Answer 25

Acetyl groups are removed, causing DNA to be more tightly wrapped around histones, increasing chromatin condensation.

Question 26

What is the role of methylation in DNA?

Answer 26

Methyl groups are added to cytosine bases, leading to decreased acetylation and making promoter regions inaccessible.

Question 27

How can epigenetic changes be inherited?

Answer 27

Environmental influences can cause changes that are passed on to offspring.

Question 28

What causes cancer at the genetic level?

Answer 28

Mutations in genes that control cell division lead to rapid, uncontrolled growth.

Question 29

What are benign tumours?

Answer 29

Non-cancerous tumours that do not invade surrounding tissues.

Question 30

What are malignant tumours?

Answer 30

Cancerous tumours that can spread to other parts of the body.

Question 31

What are proto-oncogenes?

Answer 31

Genes that stimulate cell division.

Question 32

What are tumour suppressor genes?

Answer 32

Genes that inhibit cell division and repair faulty DNA.

Question 33

What happens when a proto-oncogene mutates?

Answer 33

It becomes an oncogene and cells divide continuously.

Question 34

What is the function of the p53 protein?

Answer 34

It stops the cell cycle from moving from G1 to S phase.

Question 35

What is the significance of BRCA1 and BRCA2 genes?

Answer 35

They are tumour suppressor genes that help repair damaged DNA.

Question 36

What is the relationship between BRCA mutations and breast cancer?

Answer 36

Populations with mutated BRCA genes have an increased incidence of breast cancer.

Question 37

What is the role of proteins that help to repair damaged DNA?

Answer 37

They assist in the repair of damaged DNA.

Question 38

What is the incidence of breast cancer in women with mutations in BRCA1 or BRCA2 compared to the general population?

Answer 38

Increased incidence of breast cancer.

Question 39

What are BRCA1 and BRCA2 classified as?

Answer 39

Tumour suppressor genes.

Question 40

What happens when BRCA1 or BRCA2 genes are mutated?

Answer 40

DNA damage is not repaired, leading to uncontrolled cell division.

Question 41

What can result from uncontrolled cell division?

Answer 41

Cancer.

Question 42

What is abnormal DNA methylation, and how can it lead to cancer?

Answer 42

It can occur due to factors like smoking, leading to hypermethylation of tumour suppressor genes and hypomethylation of proto-oncogenes.

Question 43

What is the effect of hypermethylation on tumour suppressor genes?

Answer 43

It inactivates the gene, preventing transcription and translation.

Question 44

What is the outcome of hypomethylation of proto-oncogenes?

Answer 44

Permanent activation of the gene, leading to continuous cell division.

Question 45

How does increased methylation of DNA affect a tumour suppressor gene?

Answer 45

It inhibits transcription due to chromatin condensation.

Question 46

What is the effect of decreased methylation of a proto-oncogene?

Answer 46

The gene is permanently switched on, leading to excessive protein production and rapid cell division.

Question 47

How can increased levels of oestrogen lead to breast cancer?

Answer 47

Oestrogen binds to transcriptional factors, releasing inhibitors and stimulating cell division.

Question 48

What types of mutations can lead to cancer?

Answer 48

* Acquired Mutations * Hereditary Mutations

Question 49

What is a preventive measure against UV radiation?

Answer 49

Using sunscreen.

Question 50

What is one method of early diagnosis for high-risk individuals?

Answer 50

Regular screening.

Question 51

What is the complete set of genes in a cell or organism called?

Answer 51

Genome.

Question 52

What is the full range of proteins produced by a given cell called?

Answer 52

Proteome.

Question 53

What is DNA sequencing?

Answer 53

An automated procedure to determine the order of nucleotides in DNA.

Question 54

Why is determining the genome of simpler organisms easier?

Answer 54

* Most prokaryotes have a single circular DNA * DNA lacks non-coding regions

Question 55

What are potential applications of determining the genome of bacteria?

Answer 55

* Identification of antigens for vaccines * Understanding metabolic pathways for drug design

Question 56

What significant project mapped approximately 20,000 genes in the human genome?

Answer 56

The Human Genome Project.

Question 57

How long did the Human Genome Project take to complete?

Answer 57

13 years.

Question 58

What percentage of the human genome is thought to consist of coding DNA?

Answer 58

Approximately 1.5%.

Question 59

What is the aim of the Human Proteome Project?

Answer 59

To identify all the proteins produced in humans.

Question 60

the process of the of RNAi

Answer 60

double stranded RNAi is coded for my special regulatory genes, it then moves into the cytoplasm where it becomes single stranded and associates with a nucleares enzyme. it binds to a specific mRNA molecule at a specific binding site, then nuclease enzyme then cuts the mRNA in two. the mRNA can then no longer be translated so protein synthesis stops.

Question 61

the process of stimulation of gene transcription

Answer 61

transcriptional factors are found in the cytoplasm of the cell, they then move into the nucleus. the transcriptional factor binds to the promoter region of the DNA, this allows RNA polymerase to bind and transcription is is stimulated.